A common approach to lameness in the equine athlete is non-steroidal anti-inflammatory medications (NSAIDs) treatments, such as phenylbutazone (PBZ, Bute) or flunixin meglumine (FM, Banamine) alone or sometimes in combination. At the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Jonathan Foreman, DVM, MS, Dipl. ACVIM, of the University of Illinois, discussed the effect of these medications on lameness when used at a normal recommended dose with these strategies and whether combining the drugs confers any special effects.
Reversible lameness was induced in eight Thoroughbred horses by using an adjustable heart bar shoe that could be tightened with a screw to elicit severe non-weight-bearing lameness. After an hour of the shoe application, Foreman and his colleagues treated the horses with one or both drugs: PBZ at 4.4 mg/kg, FM at 1.1 mg/kg, or PBZ + FM at these same dosages. In line with findings from previous studies, the team found that peak effect of these drugs occurred four hours following administration.
The team measured heart rates as an indicator of pain since, as explained by Foreman, heart rate is a primary variable that is elevated in lame horses following exercise workouts. All NSAID treatments decreased heart rates for two to 10 hours after administration, while lameness scores decreased for 1.3-12 hours. Heart rate reduction indicative of pain relief lasted for 12 hours after giving FM alone and the combination of PBZ plus FM. Lameness scores decreased more quickly for PBZ or PBZ + FM combo-treated horses than for FM. Foreman concluded, "No significant differences were noted between giving PBZ alone or combining FM with PBZ."
Foreman reminded the veterinary audience that these drugs are not competition legal under FEI (Fédération Equestre Internationale) rules. As of Dec. 1, 2011, USEF (United States Equestrian Federation) rules allowed only one of seven USEF-approved NSAIDs, with combinations of NSAIDS no longer legal. "In an emergency such as a colic or eye injury," reported Foreman, "additional use of FM can be given at a standard dose only by a licensed veterinarian." Provided the approved paperwork is filed, the horse is allowed to compete no sooner than 24 hours later.
One of the biggest concerns he mentioned is the increased risk of gastrointestinal and renal toxicity as a result of administering PBZ and FM combination. He commented, "Recent work from another laboratory showed that combining half-dose oral PBZ with full-dose intravenous FM for only five days resulted in frequent ulcers and decreased plasma total proteins, indicative of gastrointestinal ulceration." In this current study, Foreman showed that there is no benefit in effect from combining the two drugs, and he speculated that there is very likely to be increased toxicity if that combination is given over several days time.
Foreman stressed, "Giving twice the normal dose may not cause the analgesic effect to persist up to 24 hours, while this higher dose is toxic to kidneys and an already stressed gastrointestinal tract." Since he found that combining NSAIDs achieved no better results than using either drug alone, Foreman stressed that there is no good reason to combine these NSAIDs.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.